CVE-2026-43620

import socket import struct def send_exploit_payload(client_sock): """ PoC for CVE-2026-43620 Simulates a malicious rsync server to trigger the OOB read. """ # 1. Handshake: Ensure CF_INC_RECURSE is negotiated in the protocol flags. # This requires protocol manipulation during the initial connection setup. # 2. Send Crafted File List # The first entry in the sorted list must NOT be the leading dot directory ('.') # Normally '.' is first. We send a list like ['file1', 'file2'] without '.'. # file_list_data = pack_file_list(['malicious_file']) # client_sock.send(file_list_data) # 3. Send Trigger Packet # Construct a packet with ndx=0 and iflags missing ITEM_TRANSFER. # This causes the receiver to access file_pool[-1]. ndx = 0 # Example iflags value without ITEM_TRANSFER (e.g. 0x00 or specific flags) # Assuming ITEM_TRANSFER is a specific bit not set here. iflags = 0x00 # Construct the multiplexed packet (simplified rsync protocol structure) # payload = struct.pack('>I', ndx) + struct.pack('>I', iflags) # pkt = make_rsync_packet(payload) # client_sock.send(pkt) print("[+] Exploit payload sent to trigger SIGSEGV.") # Note: This code needs to be integrated into a functioning rsync server # simulation that handles the protocol handshake to set CF_INC_RECURSE.

{"cve": {"id": "CVE-2026-43620", "sourceIdentifier": "[email protected]", "published": "2026-05-20T02:16:36.727", "lastModified": "2026-05-20T13:58:07.923", "vulnStatus": "Undergoing Analysis", "cveTags": [], "descriptions": [{"lang": "en", "value": "Rsync version 3.4.2 and prior contain a receiver-side out-of-bounds array read vulnerability in recv_files() in receiver.c that allows a malicious rsync server to crash the rsync client process. Attackers can exploit the vulnerability by setting CF_INC_RECURSE in compatibility flags and sending a specially crafted file list where the first sorted entry is not the leading dot directory, followed by a transfer record with ndx=0 and an iflag word without ITEM_TRANSFER, causing the receiver to read 8 bytes before the allocated pointer array and dereference an invalid pointer at an unmapped address, resulting in a deterministic SIGSEGV crash of the rsync client."}], "metrics": {"cvssMetricV40": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "4.0", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X", "baseScore": 6.9, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "attackRequirements": "NONE", "privilegesRequired": "NONE", "userInteraction": "ACTIVE", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "NONE", "vulnAvailabilityImpact": "HIGH", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "subAvailabilityImpact": "NONE", "exploitMaturity": "NOT_DEFINED", "confidentialityRequirement": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "availabilityRequirement": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "Safety": "NOT_DEFINED", "Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "valueDensity": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED"}}], "cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H", "baseScore": 6.5, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "REQUIRED", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 2.8, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-125"}]}], "references": [{"url": "https://github.com/RsyncProject/rsync/releases/tag/v3.4.3", "source": "[email protected]"}, {"url": "https://github.com/RsyncProject/rsync/security/advisories/GHSA-28pw-r563-rxvm", "source": "[email protected]"}, {"url": "https://www.vulncheck.com/advisories/rsync-out-of-bounds-array-read-via-recv-files", "source": "[email protected]"}]}}